Emission Computed Tomography (ECT) has been widely used in medicine for diagnosis and other purposes. Types of ECT include Positron Emission Tomography (PET) and Single-Photon Emission Computed Tomography (SPECT). A subject, such as a patient, may be scanned by an ECT scanner to obtain ECT images. When ECT is used for chest or upper abdomen examinations, respiratory motion of the lungs and/or cardiac movements of the heart of a subject may lead to motion blur in the ECT images. It is desirable to provide systems and methods for reconstructing an ECT image with improved quality and reduced motion blur.